CN114296173A

CN114296173A - Optical system

Info

Publication number: CN114296173A
Application number: CN202210036544.8A
Authority: CN
Inventors: 貟智省; 迈克尔·L·斯坦纳; 乔·A·埃特; 蒂莫西·L·翁; 吉勒·J·伯努瓦; 约翰·D·李; 埃林·A·麦克道尔; 苏珊·L·肯特
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2017-10-25
Filing date: 2018-10-19
Publication date: 2022-04-08
Also published as: US11435514B2; CN111279234B; CN111279234A; US11726249B2; US20230115202A1; JP2021500629A; WO2019082039A1; US20200284963A1; KR20200074129A

Abstract

The invention discloses an optical system, comprising: one or more optical lenses; a reflective polarizer; a partial reflector, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween; a first retarder layer disposed inside the folded optical cavity; a second retarder layer disposed outside the folded optical cavity; and a third retarder layer disposed outside the folded optical cavity and having a substantially non-uniform retardation at a predetermined wavelength such that when an image is received at an input of the optical system and detected at an output of the optical system, the image at the output of the optical system has a maximum contrast variation that is at least 5% less than an image detected at an output of a comparative optical system that does not have the third retarder layer.

Description

Optical system

The application is a divisional application based on the patent applications of 3M Innovation Co., Ltd, with the application date of 2018, 10 and 19, the application number of CN 2018800699008 (International application number of PCT/IB2018/058168) and the name of "optical retarder segment".

Technical Field

The present disclosure relates to optical systems. In particular, the present disclosure relates to optical systems including optical retarders having a plurality of segments.

Background

The optical system may utilize a reflective polarizer, a partial reflector, and a phase retarder. Such optical systems may be used in head mounted displays.

Disclosure of Invention

In some aspects of the present description, an optical system includes one or more optical lenses, a reflective polarizer, a partial reflector, a first retarder layer, a second retarder layer, and a third retarder layer. The one or more optical lenses have at least one major surface. The reflective polarizer is disposed on and conforms to the first major surface of the one or more optical lenses. The partial reflector and the reflective polarizer define a folded optical cavity therebetween. The reflective polarizer substantially reflects light having a first polarization state and substantially transmits light having an orthogonal second polarization state at a predetermined wavelength in a range from about 400nm to about 1000 nm. The partial reflector is disposed on and conforms to the second major surface of the one or more optical lenses. The partial reflector has an average optical reflectivity of at least 30% at the predetermined wavelength. A first retarder layer is disposed in the folded optical cavity, and a second retarder layer and a third retarder layer are disposed outside the folded optical cavity. The first retarder layer and the second retarder layer have a substantially uniform retardation at the predetermined wavelength, and the third retarder layer has a substantially non-uniform retardation at the predetermined wavelength.

In some aspects of the present description, the optical system described above is configured such that when an image is received at an input of the optical system and detected at an output of the optical system, the image at the output of the optical system has a maximum contrast variation that is at least 5% less than an image detected at an output of a contrast optical system without the third retarder layer.

In some aspects of the present description, the above optical system is configured such that when an image ray emitted from the display at a predetermined wavelength is first incident on the reflective polarizer, the image ray is substantially reflected at a first reflectivity (ρ), and when the image ray is again incident on the reflective polarizer, the image ray is substantially transmitted at a first transmissivity (τ), the third retarder layer increasing the first reflectivity.

In some aspects of the present description, the above-described optical system is configured such that when a uniformly polarized bright field image having a first polarization state is incident on the optical system and exits the optical system after undergoing at least one reflection at each of the reflective polarizer and the partial reflector, the exiting image fills an exit aperture, the image filling the aperture having a first image component in the first polarization state, wherein the maximum intensity of the first image component is at least 10% less than a comparative optical system without the third retarder layer.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

Drawings

In the drawings, like numbering represents like elements. Dotted lines represent optional or functional components, while dashed lines represent components outside the views.

Fig. 1 is a schematic cross-sectional view of an optical system for transmitting light.

Fig. 2 is a schematic front plan view of an optical element including discrete retarder segments.

Fig. 3A-3D are schematic front plan views of discrete retarder segments having various shapes.

Fig. 4A is a graph of the brightness ratio of bright and dark fields versus the retardance of discrete retarder segments in an optical system including discrete retarder segments.

FIG. 4B is a graph of light leakage versus retardation of discrete retarder segments in an optical system including discrete retarder segments.

FIG. 4C is a graph of power change versus retardation of a discrete retarder segment in an optical system including discrete retarder segments.

Fig. 5A is a contour plot of the brightness of a dark field image from an optical system that does not include a discrete retarder segment.

Fig. 5B is a contour plot of the brightness of a dark field image from an optical system including discrete retarder segments.

Fig. 5C is a contour plot of the brightness of a bright field image from an optical system that does not include a discrete retarder segment.

FIG. 5D is a contour plot of the brightness of a bright field image from an optical system including discrete retarder segments.

FIG. 6 is a schematic cross-sectional view of an analog optical system for transmitting light.

Fig. 7A is a schematic cross-sectional view of an analog optical system for transmitting light.

Fig. 7B is a schematic front plan view of an analog optical element including discrete retarder segments on a quarter-wave retarder.

Detailed Description

In accordance with the principles of the present disclosure, an optical system may include an optical element for improving contrast of an optical display. The optical element includes an optical surface configured to receive light of a predetermined wavelength. The optical element includes optical surface portions having a uniform retardation and optical surface portions having different retardations. The optical element includes first and second longitudinal sections that extend across opposite edges of the optical surface and have the same substantially uniform retardation for substantially normally incident light. The optical element includes four discrete retarder segments each disposed on the optical surface and having a retardation difference of substantially uniform retardation from the longitudinal segment greater than zero.

The optical element can be used in an optical system to improve the contrast of the optical system. An optical system can include a reflective polarizer layer, a partial reflector layer, a first retarder layer, a second retarder layer, and a third retarder layer, each disposed on at least one major surface of one or more optical lenses or another layer. The partial reflector and the reflective polarizer define a folded optical cavity therebetween. At a predetermined wavelength, the reflective polarizer substantially reflects light having a first polarization state and substantially transmits light having an orthogonal second polarization state. The partial reflector has an average optical reflectivity of at least 30% at the predetermined wavelength. A first retarder layer is disposed in the folded optical cavity, and a second retarder layer and a third retarder layer are disposed outside the folded optical cavity. The third retarder layer includes the above optical element.

According to the present invention, various optical defects existing in some optical systems can be corrected using an optical element having a non-uniform retardation, thereby providing improved optical performance. Polarizing components in an optical system, such as wave plates and reflective polarizers, can cause errors and misalignments in the optical system, such as by differences in the fabrication of the polarizing components or differences in the performance of the polarizing components with respect to light incident on the polarizing components at oblique angles. For example, in optical systems using standard quarter-wave retarders, there may be misalignment between the local extinction state of the reflective polarizer and the polarization state of the light ray that is first incident on the reflective polarizer and/or between the local transmission state of the reflective polarizer and the polarization state of the light ray that is again incident on the reflective polarizer. Such misalignment can occur, for example, due to the shifting of the local pass and extinction axes of the reflective polarizer when it is formed into a curved shape. As another example, in an optical system where a light source (such as a display) produces substantially non-collimated light, high angle of incidence rays may be partially absorbed or transmitted from the surface of one or more quarter-wave retarders so that contrast may be reduced.

According to the present invention, an optical element having a non-uniform retardation may retard light entering an optical system such that light rays propagating through the optical system and incident on a surface of a polarizing component associated with the exit of the optical system may more closely match a desired polarization state for polarization. For example, while light rays traveling along the optical axis may be substantially blocked or transmitted when normally incident on a surface of a reflective polarizer, light rays obliquely incident on the surface of the reflective polarizer may be partially transmitted through the reflective polarizer for an extinction state and partially reflected from the reflective polarizer layer for an on state, which may reduce the contrast ratio of the optical system. By including an optical element configured to compensate for light leakage using spatially varying non-uniform retardation, the contrast of the optical system may be increased. The optical element can be manufactured using simple manufacturing techniques. For example, the discrete retarder segments may be adhered to an optical surface, such as a quarter-wave retarder, to produce non-uniform retardation at spatial locations of the optical surface associated with the light rays that need to be compensated. As another example, the optical element may be a separate component that may be added to an existing optical system such that the optical system may be reconfigured with a different optical element (such as a particular light source having a particular field of view).

Fig. 1 is a schematic cross-sectional view of an optical system 1000 for transmitting light. Optical system 1000 includes

optical lenses

210, 410, 310, 510, and 610, a reflective polarizer layer 220 (also referred to as a "reflective polarizer"), a partial reflector layer 320 (also referred to as a "partial reflector"), a first retarder layer 420, a second retarder layer 520, and a third retarder layer 620 (also referred to as a "first retarder," "second retarder," and a "third retarder," respectively).

In the example of fig. 1, object 100 emits light 136 having a polarization state 140. After passing through the third retarder layer 620, the light ray 136 has a polarization state 141; then, after passing through the second retarder layer 520 and the partial reflector layer 320, the light ray 136 has a polarization state 142; then, after passing through the first retarder layer 420, the light ray 136 has a polarization state 143 when first incident on the reflective polarizer layer 220; then, after returning through the first retarder layer 420 and reflecting from the partial reflector layer 320, the light ray 136 has a polarization state 144; and then the light ray 136 passes through the first retarder layer 420 again into the polarization state 145 and is incident on the reflective polarizer layer 220 again. Fig. 1 also schematically shows light rays 138. Ray 138 travels along optical axis 121 and passes through retarder layer 520 at origin point 522, through retarder layer 420 at origin point 422, and through reflective polarizer 220 at origin point 221. Referring to the x-y-z coordinate system shown in FIG. 1, the polarization states 140 and 143 are shown schematically in FIG. 1 as having electric fields polarized in the x-direction. However, either or both of these polarization states may be some state other than linearly polarized in the x-direction. For example, if polarization state 141 is linearly polarized, polarization state 143 may be elliptically polarized according to the retardation of retarder layers 420, 520, 620.

Components of optical system 1000 can be disposed on one or more major surfaces of

optical lenses

210, 310, 410, 510, and 610. In other embodiments, one or more of the reflective polarizer layer 220, the partial reflector layer 320, and the retarder layers 420, 520, and 620 are disposed on a different major surface than shown in the embodiment shown in FIG. 1. For example, any one or more of the reflective polarizer layer 220, partial reflector layer 320, and

retarder layers

420, 520, and 620 may be disposed on opposing major surfaces of the respective lenses. As another example, one or more of the layers may be disposed on another of the layers. Optical lens 210 has opposing first and second

major surfaces

212, 214, optical lens 310 has opposing first and second

major surfaces

312, 314, optical lens 410 has opposing first and second

major surfaces

412, 414, optical lens 510 has opposing first and second

major surfaces

512, 514, and optical lens 610 has opposing first and second

major surfaces

612, 614.

Optical lenses

210, 310, 410, 510, 610 may be made of any suitable lens material, such as acrylic or glass. In some implementations, the optical lens is formed in an insert molding process. For example, the reflective polarizer layer 220 may be shaped into a desired shape, and then an optical lens may be insert molded onto the reflective polarizer layer 220. Any type of suitable lens may be used. In some implementations, the one or more lenses of the optical system are one of plano-convex lenses, plano-concave lenses, biconvex lenses, biconcave lenses, positive meniscus lenses, negative meniscus lenses, variable index lenses (e.g., gradient index lenses), and fresnel lenses. It will be appreciated that additional optical lenses may be included, and that many of the attributes described for one arrangement of optical lenses apply to other arrangements of optical lenses.

Optical system 1000 has an optical axis 121. An optical axis of an optical lens or optical element in an optical system, display system or optical system may be understood as an axis near the center of the system, lens or optical element through which light rays propagating along the optical axis pass with minimal refraction such that light propagating along an axis close to but different from the optical axis undergoes a greater degree of refraction. In some implementations, each of the one or more

optical lenses

210, 310, 410, 510, 610 is centered on an optical axis 121 passing through a vertex of each of the one or more

optical lenses

210, 310, 410, 510, 610. Light rays along optical axis 121 may pass through optical lenses and/or optical elements without being refracted, or substantially refracted, such that at any major surface of the optical system, the angle between a light ray incident on the surface and a light ray transmitted through the surface does not exceed 15 degrees.

In some embodiments, optical system 1000 displays object 100 to viewer 110. For example, the object 100 may be a display or an image on a display. Suitable displays include, for example, Liquid Crystal Displays (LCDs) and Organic Light Emitting Diode (OLED) displays. Alternatively, object 100 may be some object other than a display, such as an object in the environment of viewer 110. In embodiments where object 100 is a display, optical system 1000 along with the display may be referred to as a display system, or alternatively optical system 1000 may be described as including a display. In some embodiments, object 100 is a display panel that produces a polarized light output. In some embodiments, a pre-polarizer is provided that polarizes light from object 100 such that the light has polarization state 140 when incident on retarder layer 620. In some embodiments, object 100 is an object in the environment of observer 110 that emits light 136 by reflecting ambient light toward optical system 1000.

Optical system 1000 includes a reflective polarizer layer 220. In the example of fig. 1, reflective polarizer layer 220 is disposed on and conforms to major surface 214 of optical lens 210; however, in other embodiments, the reflective polarizer layer 220 may be disposed on another major surface in the optical system 1000.

The reflective polarizer layer 220 may be configured to substantially reflect light having a first polarization state and substantially transmit light having an orthogonal second polarization state at a predetermined wavelength or within a predetermined wavelength range. For example, if at least 60% of light having the first polarization state at a predetermined wavelength or within a predetermined wavelength range is reflected from the polarizer, the reflective polarizer layer 220 may be considered to substantially reflect light having the first polarization state at the predetermined wavelength or within the predetermined wavelength range. The reflective polarizer layer 220 may be considered to substantially transmit light having the second polarization state at the predetermined wavelength or within the predetermined wavelength range if at least 60% of the light having the second polarization state at the predetermined wavelength or within the predetermined wavelength range is transmitted through the reflective polarizer.

The predetermined wavelength range may be a wavelength range in which the optical system or the display system is designed to operate. The predetermined wavelength may be in a range of about 400nm to about 1000 nm. For example, the predetermined wavelength range may be a visible light range (400nm to 700 nm). As another example, the predetermined wavelength range may include one or more visible wavelength ranges. For example, the predetermined wavelength range may be a union of more than one narrow wavelength range (e.g., a union of disjoint red, green, and blue wavelength ranges corresponding to the emission color of the display panel). Such wavelength ranges are further described in U.S. patent application publication 2017/0068100(Ouderkirk et al), which is incorporated herein by reference. In some embodiments, the predetermined wavelength range includes other wavelength ranges (e.g., infrared (e.g., near infrared (about 700nm to about 2500nm)) or ultraviolet (e.g., near ultraviolet (about 300nm to about 400nm)) as well as visible wavelength ranges.

Any reflective polarizer used in any of the optical systems described herein can be a linear reflective polarizer, which can be adapted to reflect light having a first linear polarization state and transmit light having a second linear polarization state orthogonal to the first linear polarization state. Suitable reflective polarizers include, for example, polymeric multilayer optical films and wire grid polarizers. Any reflective polarizer used in any of the optical systems of the present description can be a shaped (e.g., thermoformed) reflective polarizer, which can be a thermoformed polymeric multilayer optical film. The polymeric multilayer optical film can include a plurality of alternating first polymer layers and second polymer layers. Suitable polymeric multilayer reflective polarizers are described, for example, in U.S. Pat. No. 5,882,774(Jonza et al) and U.S. Pat. No. 6,609,795(Weber et al). Methods of forming reflective polarizers into compound curves are described in U.S. patent application publication 2017/0068100(Ouderkirk et al), which is incorporated by reference above, and PCT application US2016/050024(Ouderkirk et al), which was filed 2016.9.2.2016 and the contents of which are incorporated by reference herein to the extent that they do not contradict this specification.

The reflective polarizer layer 220 may be a polymeric multilayer reflective polarizer and may have at least one layer that is substantially uniaxially oriented at the apex. In some embodiments, reflective polarizer 220 further comprises at least one layer that is substantially optically biaxial at least one first location on the at least one layer away from the optical axis and substantially optically uniaxial at least one second location away from the optical axis. The polymeric multilayer optical film can be formed (e.g., thermoformed) to provide the reflective polarizer layer 220. The optical film may initially have at least one layer uniaxially oriented with an extinction axis in the y-direction. During formation, the optical film is stretched to conform to the shape of the tool. The optical film is stretched because the desired shape is curved about two orthogonal axes. In contrast, the optical film would not need to be stretched in order to conform to a shape that is curved about only one axis. The forming process may substantially uniaxially orient the optical film at a first location (because the film is stretched in the orientation direction at that location during formation), but biaxially orient at a second location due to the optical film being stretched as it is formed.

Optical system 1000 can include a partial reflector layer 320. In the example of fig. 1, partial reflector layer 320 is disposed on and conforms to major surface 314 of optical lens 310; however, in other examples, partial reflector layer 320 may be disposed on another major surface in optical system 1000.

Partial reflector layer 320 may have any suitable reflectivity for optical system 1000. In some embodiments, the partial reflector layer 320 has an average optical reflectance and an average optical transmittance each in a range of 30% to 70% at a predetermined wavelength or within a predetermined wavelength range. For example, the partial reflector layer 320 may be a half mirror. Unless otherwise indicated, average optical reflectance and average optical transmittance within a predetermined wavelength range refer to unweighted averages over the predetermined wavelength range and polarization of optical reflectance and optical transmittance, respectively, determined at normal incidence. Unless otherwise specified, the average optical reflectance and average optical transmittance at a predetermined wavelength refer to the unweighted average of the polarization of the optical reflectance and optical transmittance, respectively, determined at normal incidence.

The partial reflector layer 320 may be any suitable partial reflector. For example, the partial reflector layer 320 may be constructed by coating a thin layer of metal (e.g., silver or aluminum) on a transparent substrate (e.g., a film that may be subsequently adhered to a lens, or the substrate may be a lens). The partial reflector layer 320 may also be formed by, for example, depositing a thin film dielectric coating onto the surface of the lens substrate, or by depositing a combination of metal and dielectric coatings onto the surface. In some implementations, the partial reflector layer 320 can be a reflective polarizer or can have a polarization dependent reflectivity. In some examples, the partial reflector layer 320 is a dielectric partial reflector layer.

The reflective polarizer layer 220 and the partial reflector layer 320 may define a folded optical cavity 700. The folded optical cavity 700 may be configured to receive light in a first polarization state at either the reflective polarizer layer 220 or the partial reflector layer 320, reflect the light at a surface of each of the reflective polarizer layer 220 and the partial reflector layer 320, and transmit the light in the first polarization state from the other of the reflective polarizer layer 220 or the partial reflector layer 320 that receives the light. By reflecting light off of both the reflective polarizer layer 220 and the partial reflector layer 320, the optical path may be compressed (i.e., "folded") in a first direction or uncompressed in a second, opposite direction, and the size of the folded optical cavity 700 may be reduced. In some examples, the folded optical cavity may be reversed such that the relative positions of reflective polarizer layer 220 and partial reflector layer 320 with respect to the viewer and object 100 may be reversed from that of exemplary optical system 1000 of fig. 1.

In some examples, the surface of optical system 1000 may include an additional anti-reflective layer. For example, an anti-reflective layer may be disposed on one of the first retarder layer 420, the second retarder layer 520, and the second major surface 212 of the optical lens 210. As another example, if either of the first or second retarder layers 420 or 520 are separate optical elements, such as shown in fig. 1, the surface of the respective retarder layer and the second major surface of the respective

optical lens

410 or 510 may be coated with an anti-reflective coating.

Optical system 1000 can include a first retarder layer 420, a second retarder layer 520, and a third retarder layer 620 (collectively, "retarder layers 420, 520, 620"). In the example of fig. 1, the first retarder layer 420 is disposed on and conforms to the major surface 414 of the optical lens 410 in the folded optical cavity 700; the second retarder layer 520 is disposed on and conforms to the major surface 514 of the optical lens 510 outside the folded optical cavity 700; and a third retarder layer 620 is disposed on and conforms to a major surface 614 of the optical lens 610 outside the folded optical cavity 700. However, in other examples, any of retarder layers 420, 520, and 620 may be disposed on another major surface in optical system 1000. For example, a first retarder layer 420 may be disposed on the reflective polarizer layer 220 opposite the major surface 214, and/or a second retarder layer 520 and a third retarder layer 620 may be disposed on the partial reflector layer 320 opposite the major surface 314.

In some implementations, any of the retarder layers 420, 520, and 620 can be disposed on a curved major surface. In some embodiments, the curved major surface is curved about one axis or curved about two orthogonal axes. In some implementations, any of the retarder layers 420, 520, and 620 can be substantially flat. A substantially flat layer may be understood to mean that the layer is nominally flat, but may have some curvature due to, for example, ordinary manufacturing variations, or may have a radius of curvature that is at least 10 times the distance from the image surface (e.g., at the display panel) to the stop surface of the optical system. In some embodiments, the third retarder layer 620 is disposed on the display panel, or on a flat substrate having no optical power.

In some cases, any of the retarder layers 420, 520, 620 may include multiple stacked retarder layers, with the multiple layers having, for example, different fast and slow axes. In this case, the effective retardation and the effective fast and slow axes of the retarder layer may be defined relative to the polarized light incident on the retarder and the polarized light transmitted through the retarder as the retardation and fast and slow axis orientations of a conventional single-layer retarder that converts the polarization state of the incident light into the polarization state of the transmitted light. The delay of such a retarder layer refers to the effective delay. For a retarder having a single layer, the effective fast and slow axes are the fast and slow axes of the single layer, and the effective retardance is the retardance of the single layer. For a retarder layer having a plurality of layers, wherein each layer has a fast axis and a slow axis parallel to or rotated 90 degrees relative to the effective fast axis and slow axis of the retarder, the effective retardation for normally incident light is the sum of the retardations of the layers having respective fast and slow axes parallel to the effective fast and slow axes of the retarder minus the sum of the retardations of the layers having respective fast and slow axes rotated 90 degrees relative to the effective fast and slow axes of the retarder.

The retarder layer used in optical system 1000 may be a film or a coating or a combination of a film and a coating. For example, suitable films include birefringent polymer film retarders, such as those available from Meadowlark Optics, Frederick, CO, fraderrick, colorado. Suitable coatings for forming the retarder layer include Linear Photopolymerizable Polymer (LPP) materials and Liquid Crystal Polymer (LCP) materials described in U.S. patent application publication 2002/0180916(Schadt et al), 2003/028048(Cherkaoui et al), 2005/0072959(Moia et al) and 2006/0197068(Schadt et al), and U.S. patent 6,300,991(Schadt et al). Suitable LPP materials include ROP-131EXP 306LPP and suitable LCP materials include ROF-5185EXP 410LCP, both available from Alice Technologies, Allschwil, Switzerland.

The first retarder layer 420 and the second retarder layer 520 may each have a substantially uniform retardation at a predetermined wavelength, such as the predetermined wavelength discussed in the context of the reflective polarizer layer 220. A retarder layer or retarder layer segment may be described as having a substantially uniform delay if the delay variation in the retarder layer is substantially less than the maximum difference in delay across the retarder. For example, a retarder having a substantially uniform delay may be understood as a retarder having a maximum difference in delay of no more than 20%.

In some examples, each of first retarder layer 420 and second retarder layer 520 may be a substantially quarter-wave retarder. A retarder layer described as a substantially quarter-wave retarder at a specified wavelength may be understood as having a retardation within 5% of 1/4% of the specified wavelength for normally incident unpolarized light of at least 80% of the surface area of the retarder layer. The retarder layer may be a substantially quarter-wave retarder at a first wavelength and have a retardation substantially different from a quarter-wave retarder at a different second wavelength. A retardation that is substantially different from a quarter wave at the second wavelength may be understood as a retardation that is not within 5% of 1/4 of the second wavelength. The quarter-wave retarders may have a spatially uniform orientation.

In some examples, retarder layers 420 and 520 have a substantially uniform optical thickness. For example, the retarder layers 420 and 520 may be constructed of the same material to provide substantially the same retardation. In some examples, retarder layer 520 has a different physical thickness than retarder layer 420. When different materials are used for different retarder layers, it may be desirable to utilize different physical thicknesses in order to have each retarder layer have approximately a quarter-wave retardation.

The third retarder layer 620 may have a non-uniform retardation. A retarder layer may be described as having a substantially non-uniform delay if its variation in delay is greater than a maximum difference in delay that represents a uniform delay, such as the uniform delay described above. For example, a retarder layer having a substantially non-uniform retardation may be understood as a retarder layer having a maximum difference in retardation of greater than 20%.

In some examples, the third retarder layer 620 may include discrete retarder sections to produce a non-uniform delay in the third retarder layer 620. Although the third retarder layer 620 as a whole may have a non-uniform retardation, each discrete retarder section may have a uniform retardation throughout the discrete retarder section. Fig. 2 is a schematic front view of an optical element 600 (such as the third retarder layer 620 of fig. 1) including discrete retarder segments.

The optical element 600 includes an optical surface 630 configured to receive light of a predetermined wavelength, such as the predetermined wavelength described in the context of the reflective polarizer layer 220. Optical surface 630 may include various surfaces of optical elements such as optical lenses, wave plates, and the like. In some examples, optical surface 630 may extend to the entire surface of the optical element, while in other examples, optical surface 630 may be limited to a portion of the optical element, such as a portion of a major surface of the optical element that receives light associated with an image. In some examples, the predetermined wavelength may be in a range of about 400nm to about 1000 nm. The optical surface 630 may be defined by a vertical axis 632 and a horizontal axis 634. The vertical axis 632 and the horizontal axis 634 may define four cartesian quadrants (I, II, III, IV). In the example of fig. 2, the cartesian quadrants are numbered sequentially in a counterclockwise direction.

The optical surface 630 may include a first longitudinal section 636, the first longitudinal section 636 being substantially centered on the vertical axis 632 and a second longitudinal section 638, the second longitudinal section 638 being substantially centered on the horizontal axis 634. The first longitudinal section 636 and the second longitudinal section 638 may each extend across opposite edges of the optical surface. The first longitudinal section 636 and the second longitudinal section 638 may represent a portion of the optical element 600 configured to receive light rays that may not require compensation. For example, a light ray incident on the first longitudinal section 636, the second longitudinal section 638, or both, may propagate through the optical system 1000 such that the light ray is substantially unaffected by misalignments within the optical system 1000.

The first longitudinal section 636 and the second longitudinal section 638 may have the same substantially uniform retardation (δ) for substantially normal incident light. A substantially uniform delay may be understood as the maximum variation in delay in each of the first longitudinal section 636 and the second longitudinal section 638 (the maximum delay minus the minimum delay in that region) may be no more than 10% of the maximum variation in delay in the respective longitudinal section. In examples where optical surface 630 is a surface of an optical lens, the substantially uniform retardation may be zero. In examples where optical surface 630 is a surface of a quarter-wave retarder (such as second retarder layer 520), the substantially uniform retardation may be the quarter-wave retardation of second retarder layer 520. In some examples, the first longitudinal section 636 and the second longitudinal section 638 cover at least 10% of the surface area of the optical surface 630.

The third retarder layer 620 may include a plurality of discrete retarder segments. The discrete retarder segments may be one retarder segment covering one discrete segment of the optical surface 630. In some examples, the plurality of discrete retarder segments may be physically discrete such that there are no two retarder segments in physical contact. In some examples, two or more of the plurality of discrete retarder segments may be in physical contact or physical engagement, but may cover discrete portions of the optical surface 630.

In the example of fig. 2, the third retarder layer 620 includes four separate retarder sections, including a first retarder section 620A, a second retarder section 620B, a third retarder section 620C, and a fourth retarder section 620D. Each

discrete retarder segment

620A, 620B, 620C, 620D may be disposed on a respective cartesian quadrant I, II, III, IV of the optical surface 630.

Each discrete retarder segment may have a retardation difference θ with a substantially uniform retardation δ of the first and second

longitudinal segments

626 and 628, the retardation difference θ being greater than zero. In some examples, each

discrete retarder segment

620A, 620B, 620C, 620D has a substantially uniform retardation difference from the substantially uniform retardation of the first longitudinal segment 626 and the second longitudinal segment 628. For example, each

discrete retarder segment

620A, 620B, 620C, 620D may have a delay difference of at least about 0.2 λ from the delay of the first longitudinal segment 626 and the second longitudinal segment 628.

In some examples, the retardation difference of the discrete retarder sections may be selected according to a number of factors, including but not limited to ghost images, contrast, light leakage, optical power, and the like. For example, as shown in fig. 4A-4C, while contrast and dark field leakage may increase with increasing retardation difference of the discrete retarder segments, the optical power may decrease for the bright field. For certain applications, the reduction in light leakage and the increase in contrast may be balanced with, for example, a reduction in bright field brightness. In some examples, the delay difference is less than about 0.2 λ. For example, 0.2 λ may advantageously be associated with improved contrast while maintaining sufficient optical power and/or brightness. In some examples, the delay difference may be less than about 0.1 λ. For example, for a folded optical system with a small field of view, 0.1 λ may be advantageously associated with improved contrast.

The delay difference θ may be a positive delay difference θ + or a negative delay difference θ -. Whether a discrete retarder section includes a positive or negative retardation difference may depend on the desired polarization state of light passing through optical system 1000. For example, a particular discrete retarder segment of the third retarder layer 620 may have a positive retardation difference if clockwise elliptical polarization is desired, and a negative retardation difference if counterclockwise elliptical polarization is desired. In some examples, two discrete retarder segments of the third retarder layer 620 may have a positive retardation difference θ + from the retardation δ of the first longitudinal segment 636 and the second longitudinal segment 638 and two other discrete retarder segments of the third retarder layer 620 may have a negative retardation difference θ -from the retardation δ of the first longitudinal segment 636 and the second longitudinal segment 638. For example, the first and third

discrete retarder sections

620A and 620C may have a retardation difference of +0.2 λ from the retardation of the first and second

longitudinal sections

636 and 638, and the second and fourth

discrete retarder sections

620B and 620D may have a retardation difference of-0.2 λ from the retardation of the first and second

longitudinal sections

636 and 638, or vice versa.

It should be understood that the delay may mean the average delay of a particular

individual retarder section

620A, 620B, 620C, 620D or

longitudinal section

636, 638. For example, for a particular wavelength, the first longitudinal section 636 and the second longitudinal section 638 may have an average delay substantially equal to δ, while each

discrete retarder section

620A, 620B, 620C, 620D may have an average delay substantially equal to θ + (such as for the second discrete retarder section 620B and the fourth discrete retarder section 620D), or an average delay substantially equal to θ — (such as for the first discrete retarder section 620A and the third discrete retarder section 620C).

The retardation of the third retarder layer 620 may be related to the optical thickness. The optical thickness of the retarder layer for a given effective fast or slow axis is defined as the refractive index of each layer of the retarder along the given effective fast or slow axis multiplied by the thickness of that layer and then summed. In some examples, the first longitudinal section 636 and the second longitudinal section 638 each have the same substantially uniform optical thickness Λ. In some examples, each of the discrete retarder segments has an optical thickness difference ε that is greater than zero from the substantially uniform optical thickness Λ of the first longitudinal segment 636 and the second longitudinal segment 638. In some examples, two discrete retarder segments of the third retarder layer 620 may have a positive optical thickness difference, ε +, from the optical thicknesses, Λ, of the first and second

longitudinal segments

636, 638 and two other discrete retarder segments of the third retarder layer 620 may have a negative optical thickness difference, ε -, from the optical thicknesses, Λ, of the first and second

longitudinal segments

636, 638.

The relative sizes of the

discrete retarder segments

620A, 620B, 620C, 620D can be described in terms of the surface area of the optical surface 630 determined from a plan view of a plane orthogonal to the optical axis. In some implementations, in plan view, the optical surface 630 has an area a such that the

discrete retarder segments

620A, 620B, 620C, 620D have a combined area in a range of about a/10 to about 2A/3, and each of the

discrete retarder segments

620A, 620B, 620C, 620D has an area in a range of about a/40 to about a/6. In some examples, each

discrete retarder segment

620A, 620B, 620C, 620D covers at least 20% of the surface area of each respective cartesian quadrant I, II, III, IV of the optical surface 630. In some examples, the surface coverage of the

discrete retarder sections

620A, 620B, 620C, 620D may be related to the field of view of the display 880, such that as the field of view increases, the surface coverage of each of the

discrete retarder sections

620A, 620B, 620C, 620D increases.

The individual retarder segments of the third retarder layer 620 may have a variety of shapes. Fig. 3A-3D are schematic front plan views of discrete retarder segments having various shapes. Fig. 3A shows a discrete retarder segment 622 having a right-triangle shape that includes a right angle and equal catheti. For example, discrete retarder segments 622 may be used for optical surfaces that receive square images. Fig. 3B shows a discrete retarder segment 624 having a right-triangle shape that includes a right angle and unequal legs. For example, the discrete retarder segments 624 may be used for optical surfaces that receive wide-angle images. Fig. 3C shows a discrete retarder segment 626 having a quarter-circle shape that includes a right angle, equal square edges, and rounded hypotenuses. For example, discrete retarder segments 626 may be used for curved optical surfaces. Fig. 3D shows a discrete retarder segment 628 having an inverted quarter-circle shape that includes a right angle, equal catheti, and a concave hypotenuse. Other shapes that may be used include, but are not limited to, circles, squares, triangles, and the like. For example, a full shape may be used instead of a quarter circle, as shown in FIG. 7B. Factors that may be used to select the shape of the

discrete retarder sections

620A, 620B, 620C, and 620D may include, but are not limited to, the field of view, the shape of the display 100, the angle of incidence of the light, and the like.

In some implementations, the

discrete retarder sections

620A, 620B, 620C, 620D can be shaped to substantially cover the perimeter of the optical surface 630. The

discrete retarder segments

620A, 620B, 620C, 620D can be considered to substantially cover the perimeter around the optical surface 630 if the

discrete retarder segments

620A, 620B, 620C, 620D cover at least 50% of the perimeter of the optical surface 630. For example, in the example of fig. 2, the

discrete retarder segments

620A, 620B, 620C, 620D cover at least 80% of the perimeter of the optical surface 630, while in the example of fig. 7B, the

discrete retarder segments

810A, 810B, 810C, 810D cover about 70% of the perimeter of the second retarder layer 820.

It should be understood that the properties of optical element 600 described for one optical system (e.g., non-uniform retardation across discrete retarder segments) also apply to other optical systems corresponding to that optical system but having a different number of optical lenses or having various layers disposed on different major surfaces of one or more optical lenses. Although the third retarder layer 620 has been described as being disposed on an optical surface of the optical lens 610 as the optical element 600, the third retarder layer 620 may be disposed on various optical surfaces. For example, the third retarder layer 620 may be disposed on an optical surface of a retarder, such as the second retarder layer 520. In some examples, third retarder layer 620 may be disposed on a quarter-wave retarder such that third retarder layer 620 and the quarter-wave polarizer may be used with, for example, a folded optical cavity (such as folded optical cavity 700).

The

discrete retarder segments

620A, 620B, 620C, 620D may be disposed on the optical surface using a variety of methods including, but not limited to, atomic layer deposition, adhesion, and any other technique that can form discrete retarder segments on an optical surface. In some examples, the discrete retarder segments may be formed separately from and adhered to the optical surface. In some examples, a method for manufacturing the optical element 600 includes coupling four

discrete retarder segments

620A, 620B, 620C, 620D to the optical surface 630 such that the optical surface includes a first longitudinal segment 636 and a second longitudinal segment 638, each of the first longitudinal segment 636 and the second longitudinal segment 638 extending across opposing edges of the optical surface 630 and having a same substantially uniform retardation δ for substantially normally incident light. For example, the discrete retarder segments may be formed as a retarder layer having a uniform retardation equal to the retardation difference θ and shaped. The discrete retarder segments may be positioned on the optical surface 630 in a desired configuration. For example, two discrete retarder segments may be positioned at two opposing corners of optical surface 630 such that the two discrete retarder segments have a positive retardation difference θ +, while two other discrete retarder segments may be positioned at two other opposing corners of optical surface 630 such that the two other discrete retarder segments have a negative retardation difference θ -. The discrete retarder segments may be adhered to the optical surface 630, for example, by using an optical adhesive.

Optical element 600 can be used in an optical system, such as optical system 1000 of fig. 1, to improve contrast. For example, object 100 may define an input end of optical system 1000, and user 110 may define an output end of optical system 1000. An image received at an input of optical system 1000 may be detected at an output of optical system 1000. The image detected at the output of the optical system 1000 may have contrast variations. For example, in fig. 5B and 5D, images 784B and 784D, respectively, have brightness variations that collectively define a contrast, where contrast is defined as bright field brightness/dark field brightness. While the bright field brightness of image 784D may be fairly uniform, the dark field brightness of image 784B is very non-uniform, causing a large change in contrast.

In some examples, third retarder layer 620 may be configured such that when the image is received at the input of optical system 1000 and detected at the output of optical system 1000, the image at the output of optical system 1000 has a maximum contrast change that is at least 5% less than the image detected at the output of a contrast optical system without the third retarder layer. For example, in fig. 5A and 5C, images 784A and 784C have brightness variations that define contrast, respectively. As shown in the examples of fig. 5A-5D, while a compensating retarder layer, such as the third retarder layer 620, may reduce the brightness of portions of an image in the bright state, the compensating retarder layer may significantly reduce the brightness of portions of an image in the dark state such that the contrast variation is less than a contrast optical system without the compensating retarder layer 810.

Optical element 600 can be used in an optical system, such as optical system 1000 of fig. 1, to improve the reflectivity of light rays incident on the reflective polarizer of the optical system. For example, a light ray 136 emitted from the object 100 may first be incident on the reflective polarizer layer 220 and substantially reflected back at the first reflectivity (ρ). When the light ray 136 is again incident on the reflective polarizer layer 220, the light ray 136 may be substantially transmitted at the first transmittance (τ).

In some examples, the third retarder layer 620 may be configured such that when image light emitted from the display at a predetermined wavelength is first incident on the reflective polarizer, the image light is substantially reflected at a first reflectivity (ρ), and when image light is again incident on the reflective polarizer, the image light is substantially transmitted at a first transmissivity (τ), the third retarder layer increasing the first reflectivity. As described above, third retarder layer 620 may compensate for misalignments that may result in a phase shift of a polarization state in an optical system. The third retarder layer 620 may phase shift light such that light first incident on the reflective polarizer layer 220 may be more precisely aligned with the extinction state of the reflective polarizer layer 220 such that light may be reflected and the reflective polarizer may have a higher reflectivity than a comparative optical system without the third retarder layer 620. In some examples, adding the third retarder layer 620 to the optical system does not significantly change the first transmittance. For example, substantially the same amount of light may be transmitted, although the reflectivity may be increased.

Optical element 600 can be used in an optical system, such as optical system 1000 of fig. 1, to reduce light leakage in the optical system for undesired output polarization states. A reduction in light leakage may be indicated by a reduction in the maximum intensity of the polarization component of the image processed by the optical system. In some examples, third retarder layer 620 may be configured such that when a uniformly polarized bright field image is incident on optical system 1000 and exits optical system 1000 after undergoing at least one reflection at each of reflective polarizer layer 220 and partial reflector layer 320, the exiting image light fills an exit aperture, the image filling the aperture having a first image component in a first polarization state, wherein the maximum intensity of the first image component is at least 10% less than a comparative optical system without the third retarder layer. For example, FIG. 4C shows that the optical power decreases as the retardation of the compensating retarder layer 810 of FIG. 7A increases.

Examples

Example 1: folded optical system simulation

FIG. 6 is a schematic cross-sectional view of an analog optical system for transmitting light. Surface 720 may represent the surface of a light emitting object. Light propagating through the optical system may pass through surfaces 730, 740, and 750, reflect off surface 760, pass through surface 750, reflect off surface 740, pass through surfaces 750 and 760, and be emitted on surface 770. The optical system of fig. 6 may have the following properties, as shown in table 1 below:

TABLE 1

Example 2: light leakage compensation simulation using folded optical systems with discrete retarder segments

Fig. 7A is a schematic cross-sectional view of an analog optical system 800 for transmitting light. Optical system 800 includes a second quarter-wave retarder layer 820, a partial reflector layer 830, a first quarter-wave retarder layer 840 and a reflective polarizer layer 850, a display 880, and a pre-polarizer 890. The optical system 800 may optionally include a compensating retarder layer 810 and/or an absorbing polarizer 860, depending on the test configuration, as will be described below. The display 880 may emit light to a simulated eye 870 having an aperture 872 to form an image 874. Each of the first quarter-wave retarder layer 840, the second quarter-wave retarder layer 820, and the compensating retarder layer 810 are modeled as having a substantially uniform retardation across the respective retarder layer. The components of fig. 7A may correspond to similar components of fig. 1. For example, the compensating retarder layer 810 may correspond to the third retarder layer 620, the second quarter-wave retarder layer 820 may correspond to the second retarder layer 520, the first quarter-wave retarder layer 840 may correspond to the first retarder layer 420, the partial reflector layer 830 may correspond to the partial reflector layer 320, the reflective polarizer layer 850 may correspond to the reflective polarizer layer 220, and the display 880 and the pre-polarizer 890 may correspond to the display 100.

The absorbing polarizer 860 may be configured to produce either a bright field image for the image 874 or a dark field image for the image 874. For example, in a bright field image configuration, the absorbing polarizer 860 may be aligned with the polarization state of light emitted from the reflective polarizer layer 850 such that the image 874 is a bright field image. Alternatively, the absorbing polarizer may be removed from the optical system 800. In a dark field image configuration, the absorbing polarizer 860 may be crossed or staggered by approximately 90 ° from the polarization state of the light emitted from the reflective polarizer layer 850, such that the image 874 is a dark field image.

The compensating retarder layer 810 may be included in or removed from the optical system 800 to implement a compensating optical system or an uncompensated optical system, respectively, in order to produce a compensated image or an uncompensated image, respectively. Fig. 7B is a schematic front plan view of a compensating retarder layer 810 overlapping a second quarter-wave retarder layer 820. The compensated retarder layer 810 may include four circular

discrete retarder segments

810A, 810B, 810C, and 810D.

Optical system 800 was tested in different configurations of absorbing polarizer 860 and compensating retarder layer 810, for a total of four configurations: an absorbing polarizer 860 and an uncompensated retarder layer 810 for an uncompensated dark field image 874A; an absorbing polarizer 860 and a compensating retarder layer 810 for compensated dark field image 874B; an non-absorbing polarizer 860 and an uncompensated retarder layer 810 for an uncompensated bright field image 874C; and no absorbing polarizer 860 and compensating retarder layer 810 for the compensated bright field image 874D. For each configuration that includes the compensated retarder layer 810, the retardation of the compensated retarder layer 810 varies from zero to about 0.275 λ.

Example 2A: an absorbing polarizer; uncompensated retarder layer

Fig. 5A is a contour plot of the brightness of uncompensated dark field image 874A from optical system 800 that does not include compensated retarder layer 810 and includes absorbing polarizer 860. Uncompensated dark field image 874A includes regions of relatively high brightness. For example, the corners of uncompensated dark field image 874 associated with higher incident angle light have up to 1.5 × 10^- ⁶W/mm²While the central region of uncompensated dark field image 874A has a brightness of about 0W/mm²The brightness of (2).

Example 2B: an absorbing polarizer; compensating retarder layer

FIG. 5B is the contour of the brightness of compensated dark field image 874B from optical system 800 including compensated retarder layer 810 and absorbing polarizer 860And (6) line drawing. Compensated dark field image 874B includes regions of relatively lower brightness than the uncompensated dark field image 874A of fig. 5A. For example, the corners of compensated dark field image 874B have a height of up to 5.5 × 10^-7W/mm²And the central region of compensated dark field image 874B has about 0W/mm²The brightness of (2).

Example 2C: a non-absorbing polarizer; uncompensated retarder layer

Fig. 5C is a contour plot of the brightness of an uncompensated bright field image 874C from an optical system 800 that does not include the compensating retarder layer 810 or the absorbing polarizer 860. The uncompensated bright field image 874C includes regions of relatively uniform high brightness. For example, the corners of the uncompensated bright field image 874 associated with higher incident angle light have up to about 7 x 10^-5W/mm²While the central area of the uncompensated bright field image 874C has a brightness of about 1 x 10^-4W/mm²The brightness of (2).

Example 2D: a non-absorbing polarizer; compensating retarder layer

Fig. 5D is a contour plot of the brightness of a bright field image from an optical system 800 that includes the compensating retarder layer 810 and does not include the absorbing polarizer 860. The compensated bright field image 874D includes regions of relatively lower brightness than the uncompensated bright field image 874C of fig. 5C, but without a significant decrease in the retardation difference used to compensate the retarder layer 810. For example, the corners of the compensated bright field image 874D associated with higher incident angle light have up to about 5 × 10^-5W/mm²And the center area of the compensated bright field image 874D has a brightness of about 1 x 10^-4W/mm²The brightness of (2).

To determine the compensated contrast of the image of the optical system 800, the brightness of the bright field image 874D may be compared to the brightness of the dark field image 874B. FIG. 4A is a graph of the luminance ratio (representing contrast) of the bright field image 874B and dark field image 874D in an optical system 800 including a compensated retarder layer 810 versus the retardation of the

discrete retarder sections

810A, 810B, 810C, 810D of the compensated retarder layer 810. As shown in fig. 4A, the contrast of the image 874 increases as the delay of the compensated retarder layer 810 increases.

To determine the light leakage of optical system 800 in the dark state, the brightness of dark field image 874B at various retardations of compensated retarder layer 810 can be evaluated. Fig. 4B is a graph of light leakage of compensated dark field image 874B in optical system 800 including compensated retarder layer 810 versus retardation of

discrete retarder segments

810A, 810B, 810C, 810D of compensated retarder layer 810. As shown in fig. 4B, the leakage light decreases as the retardation of the compensating retarder layer 810 increases.

To determine the brightness of optical system 800 in the bright state, the brightness of bright field image 874D at various delays of compensated retarder layer 810 may be evaluated. Fig. 4C is a graph of the optical power of the compensated bright field image 874D in the optical system 800 including the compensated retarder layer 810 versus the retardation of the

discrete retarder segments

810A, 810B, 810C, 810D of the compensated retarder layer 810. As shown in fig. 4C, the optical power gradually decreases with increasing retardation of the compensating retarder layer 810, indicating that the retardation of the compensating retarder layer 810 can be controlled to balance, for example, higher contrast with reduced bright field image brightness.

The following is a list of embodiments of the present disclosure:

embodiment 1 is an optical element comprising: an optical surface configured to receive light at a predetermined wavelength λ in a range of about 400nm to about 1000nm, the optical surface defined by a vertical axis and a horizontal axis, the vertical axis and the horizontal axis defining four cartesian quadrants sequentially numbered in a counterclockwise direction; a first longitudinal section substantially centered on the vertical axis; a second longitudinal section substantially centered on the horizontal axis, the first and second longitudinal sections each extending across opposite edges of the optical surface and having a same substantially uniform retardation δ for substantially normally incident light; and four discrete retarder segments, each retarder segment disposed on a respective cartesian quadrant of the optical surface, wherein each discrete retarder segment has a retardation difference θ from δ greater than zero.

Embodiment 2 is the optical element of embodiment 1, wherein θ is less than about 0.2 λ.

Embodiment 3 is the optical element of embodiment 1 or 2, wherein θ is less than about 0.1 λ.

Embodiment 4 is the optical element of any one of embodiments 1-3, wherein each discrete retarder segment has a substantially uniform retardation difference θ from δ.

Embodiment 5 is the optical element of any one of embodiments 1 to 4, wherein each discrete retarder segment covers at least 20% of a surface area of each respective cartesian quadrant of the optical surface.

Embodiment 6 is the optical element of any one of embodiments 1-5, wherein the first and third discrete retarder sections have a retardation difference θ + greater than δ and the second and fourth discrete retarder sections have a retardation difference θ -less than δ.

Embodiment 7 is the optical element of any one of embodiments 1 to 6, wherein the first longitudinal section and the second longitudinal section cover at least 10% of the surface area of the optical surface.

Embodiment 8 is the optical element of any one of embodiments 1 to 7, wherein the first longitudinal section and the second longitudinal section each have a same uniform optical thickness Λ, and each discrete retarder section has an optical thickness difference ε from Λ that is greater than zero.

Embodiment 9 is the optical element of embodiment 8, wherein the first and third discrete retarder sections have an optical thickness difference, epsilon +, greater than Λ and the second and fourth discrete retarder sections have a retardation difference, epsilon-, less than Λ.

Embodiment 10 is the optical element of any one of embodiments 1-9, wherein each discrete retarder segment is a right triangle.

Embodiment 11 is the optical element of any one of embodiments 1-10, wherein each discrete retarder segment is quarter-circular.

Embodiment 12 is the optical element of any one of embodiments 1-11, wherein each discrete retarder segment is an inverted quarter-circle.

Embodiment 13 is the optical element of any one of embodiments 1 to 12, further comprising a retarder disposed on the optical lens, wherein the optical surface is a portion of a major surface of the retarder.

Embodiment 14 is the optical element of embodiment 13, wherein the retarder is a quarter-wave retarder.

Embodiment 15 is the optical element of any one of embodiments 1 to 14, wherein the optical surface is a curved surface.

Embodiment 16 is an optical system for transmitting light, the optical system comprising: one or more optical lenses having at least one major surface; a reflective polarizer disposed on and conforming to a first major surface of the one or more optical lenses, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal second polarization state at a predetermined wavelength in a range of about 400nm to about 1000 nm; a partial reflector disposed on and conforming to a second major surface of the one or more optical lenses, the partial reflector having an average optical reflectivity of at least 30% at the predetermined wavelength, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween; a first retarder layer disposed inside the folded optical cavity; a second retarder layer disposed outside the folded optical cavity; and a third retarder layer comprising the optical element according to any one of embodiments 1 to 13.

Embodiment 17 is the optical system of embodiment 16, wherein the first retarder layer and the second retarder layer have substantially uniform retardation at the predetermined wavelength.

Embodiment 18 is the optical system of embodiment 16 or 17, wherein the first retarder layer and the second retarder layer have a substantially uniform optical thickness.

Embodiment 19 is the optical system of any one of embodiments 16-18, wherein only one of the first, second, and third retarder layers includes an anti-reflective coating.

Embodiment 20 is the optical system of any one of embodiments 16 to 19, wherein at least one major surface of the one or more optical lenses is a curved surface.

Embodiment 21 is an optical system, comprising: one or more optical lenses having at least one major surface; a reflective polarizer disposed on and conforming to a first major surface of the one or more optical lenses, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal second polarization state at a predetermined wavelength in a range of about 400nm to about 1000 nm; a partial reflector disposed on and conforming to a second major surface of the one or more optical lenses, the partial reflector having an average optical reflectivity of at least 30% at the predetermined wavelength, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween; a first retarder layer disposed inside the folded optical cavity and having a substantially uniform retardation at the predetermined wavelength; a second retarder layer disposed outside the folded optical cavity and having a substantially uniform retardation at a predetermined wavelength; and a third retarder layer disposed outside the folded optical cavity and having a substantially non-uniform retardation at the predetermined wavelength such that when an image is received at an input of the optical system and detected at an output of the optical system, the image at the output of the optical system has a maximum contrast variation that is at least 5% less than an image detected at an output of a contrast optical system without the third retarder layer.

Embodiment 22 is the optical system of embodiment 21, wherein the third retarder layer comprises the optical element of any one of embodiments 1-15.

Embodiment 23 is the optical system of embodiment 21 or 22, wherein only one of the first retarder layer, the second retarder layer, and the third retarder layer comprises an anti-reflective coating.

Embodiment 24 is the optical system of any one of embodiments 21-23, wherein at least one major surface of the one or more optical lenses is a curved surface.

Embodiment 25 is an optical system for displaying an object to a viewer, the optical system comprising: one or more optical lenses having at least one curved major surface; a reflective polarizer disposed on and conforming to a first major surface of the one or more optical lenses, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal polarization state at a predetermined wavelength in a range of about 400nm to about 1000 nm; a partial reflector disposed on and conforming to a second, different major surface of the one or more optical lenses, the partial reflector having an average optical reflectivity of at least 30% at a predetermined wavelength, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween; a first retarder layer disposed inside the folded optical cavity and having a substantially uniform retardation at the predetermined wavelength; a second retarder layer disposed outside the folded optical cavity and having a substantially uniform retardation at a predetermined wavelength; and a third retarder layer disposed outside the folded optical cavity and having a substantially non-uniform retardation at the predetermined wavelength such that image light emitted from the display at the predetermined wavelength is substantially reflected at a first reflectivity (ρ) when the image light is first incident on the reflective polarizer and substantially transmitted at a first transmissivity (τ) when the image light is again incident on the reflective polarizer, the third retarder layer increasing the first reflectivity.

Embodiment 26 is the optical system of embodiment 25, wherein the third retarder layer does not change the first transmittance.

Embodiment 27 is the optical system of embodiment 25 or 26, wherein the third retarder layer comprises the optical element of any one of embodiments 1-15.

Embodiment 28 is the optical system of any one of embodiments 25-27, wherein only one of the first, second, and third retarder layers includes an anti-reflective coating.

Embodiment 29 is the optical system of any one of embodiments 25-28, wherein at least one major surface of the one or more optical lenses is a curved surface.

Embodiment 30 is an optical system, comprising: one or more optical lenses having at least one major surface; a reflective polarizer disposed on and conforming to a first major surface of the one or more optical lenses, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal second polarization state at a predetermined wavelength in a range of about 400nm to about 1000 nm; a partial reflector disposed on and conforming to a second major surface of the one or more optical lenses, the partial reflector having an average optical reflectivity of at least 30% at the predetermined wavelength, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween; a first retarder layer disposed inside the folded optical cavity and having a uniform retardation at the predetermined wavelength; a second retarder layer disposed outside the folded optical cavity and having a uniform retardation at the predetermined wavelength; and a third retarder layer disposed outside the folded optical cavity and having a non-uniform retardation at the predetermined wavelength such that when a uniformly polarized bright field image having a first polarization state is incident on the optical system and exits the optical system after undergoing at least one reflection at each of the reflective polarizer and the partial reflector, the exiting image fills an exit aperture, the image filling the aperture having a first image component in the first polarization state, wherein a maximum intensity of the first image component is at least 10% less than a comparative optical system without the third retarder layer.

Embodiment 31 is the optical system of embodiment 30, wherein the third retarder layer comprises the optical element of any one of embodiments 1-15.

Embodiment 32 is the optical system of embodiment 30 or 31, wherein only one of the first, second, and third retarder layers comprises an anti-reflective coating.

Embodiment 33 is the optical system of any one of embodiments 30 to 32, wherein at least one major surface of the one or more optical lenses is a curved surface.

Embodiments of various embodiments of the present invention have been described. These and other embodiments are within the scope of the following claims.

Claims

1. An optical system, comprising:

one or more optical lenses having at least one major surface;

a reflective polarizer disposed on and conforming to a first major surface of the one or more optical lenses, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal second polarization state at a predetermined wavelength in a range from about 400nm to about 1000 nm;

a partial reflector disposed on and conforming to a second major surface of the one or more optical lenses, the partial reflector having an average optical reflectivity of at least 30% at the predetermined wavelength, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween;

a first retarder layer disposed inside the folded optical cavity and having a substantially uniform retardation at the predetermined wavelength;

a second retarder layer disposed outside the folded optical cavity and having a substantially uniform retardation at the predetermined wavelength; and

a third retarder layer disposed outside the folded optical cavity and having a substantially non-uniform retardation at the predetermined wavelength,

such that when an image is received at an input of the optical system and detected at an output of the optical system, the image at the output of the optical system has a maximum contrast variation that is at least 5% less than an image detected at an output of a contrast optical system that does not have the third retarder layer.

2. The optical system of claim 1, wherein the at least one major surface of the one or more optical lenses is a curved surface.

3. An optical system for displaying an object to a viewer, comprising:

one or more optical lenses having at least one curved major surface;

a reflective polarizer disposed on and conforming to a first major surface of the one or more optical lenses, the reflective polarizer substantially reflecting light having a first polarization state and substantially transmitting light having an orthogonal polarization state at a predetermined wavelength in a range from about 400nm to about 1000 nm;

a partial reflector disposed on and conforming to a second, different major surface of the one or more optical lenses, the partial reflector having an average optical reflectivity of at least 30% at the predetermined wavelength, the partial reflector and the reflective polarizer defining a folded optical cavity therebetween;

such that when image light emitted from the display at the predetermined wavelength is first incident on the reflective polarizer, the image light is substantially reflected at a first reflectivity (p) and when the image light is again incident on the reflective polarizer, the image light is substantially transmitted at a first transmissivity (τ), the third retarder layer increasing the first reflectivity.

4. An optical system, comprising:

one or more optical lenses having at least one major surface;

a first retarder layer disposed inside the folded optical cavity and having a uniform retardation at the predetermined wavelength;

a second retarder layer disposed outside the folded optical cavity and having a uniform retardation at the predetermined wavelength; and

a third retarder layer disposed outside the folded optical cavity and having a non-uniform retardation at the predetermined wavelength,

such that when a uniformly polarized bright field image having the first polarization state is incident on the optical system and exits the optical system after undergoing at least one reflection at each of the reflective polarizer and the partial reflector, the exiting image fills an exit aperture, the image filling the aperture having a first image component in the first polarization state, wherein the maximum intensity of the first image component is at least 10% less than a comparative optical system without the third retarder layer.